1. Field of the Invention
The present invention relates to a process for preparing high-softening point pitch rich in mesopores and a high-softening-point pitch prepared thereby, and a process for preparing carbonaceous material carrying ultrafinely dispersed metal.
2. Description of the Prior Art
Carbonaceous materials carrying a metal have conventionally been utilized as catalysts for various reactions. In recent years, various carbonaceous materials carrying a metal with new functions have been developed. Examples of such carbonaceous materials include a deodorant comprising metallic silver or manganese carried on activated carbon which possesses the function of decomposing bad odors; an adsorbent obtained by carbonizing or activating an organic material containing a metal complex which is useful for adsorbing and separating saccharides, vitamine, dyes, and macro-molecules such as humus contained in raw city water; and an iron-containing carbonaceous magnetic material obtained by decomposing an organic material containing iron. It is expected that application of these carbonaceous materials utilizing these new functions will expand in the future.
A method comprising impregnating activated carbon with an aqueous solution of a metal salt has generally been known as the method for causing a metal to be carried on carbon. Because the crystal and pore structures of carbon are dominated by the type of activated carbon used in this method, it was difficult to intentionally control the crystal and pore structures to provide target functions with the carbonaceous material.
Therefore, several methods have been proposed for controlling homogeneous metal dispersion and minute pore structure by heat treatment of these materials after the metal has been carried on, or in the presence of a metal.
Examples of such methods include a method for producing a mixture of a metal oxide with a ultrafine diameter and an organic substance such as phenol resin, subjecting the mixture to dry distillation under heating, and then carbonizing the resulting product (U.S. Pat. No. 4,970,189); a method for coordinating a metal on a high-molecular-weight compound containing an atomic group which has coordination ability in the main chain and/or side chains, and treating the resulting high-molecular-weight organic compound containing metal with heat (Japanese Patent Application Laid-opens No. He 2(1990)-6309, No. Hei 2(1990)-6310, No. Hei 2(1990)-6311, No. Hei 2(1990)-6312, No. Hei 2(1990)-6313); and a method comprising producing a mixture of pitch and an organometallic compound and stabilizing this mixture, followed by activation or carbonization (Japanese Patent Application Laid-open No. Hei 3(1991)-265510).
These methods, however, have some drawbacks. For example, it is difficult to obtain a homogeneously dispersed ultrafine metallic compound in an organic substance, because the ultrafine particles of metallic compound may agglomerate and precipitate during the operation. The organic metal complex soluble in an organic solvent or in pitch which is used in these methods is an expensive, special complex. An increase in the production cost of the resulting carbonaceous material is thus unavoidable.
Moreover, the following methods using raw materials which are obtained from heavy oil have been proposed as methods for producing carbonaceous materials carrying a metal: a method comprising oxidizing a mesophase pitch by an oxidizing agent such as nitric acid, preparing a mixture of the resulting aromatic condensation compound possessing a hydrophilic group, a solution of a metal salt, and an alkaline aqueous solution, and decomposing this mixture of alkaline aqueous solution (Japanese Patent Application Laid-open No. Hei 5(1993)-59414); a method comprising treating a carbonaceous bituminous material with an oxidizing agent to introduce a functional group, dissolving the resulting product in a specific organic solvent, adding an organic metal complex dissolvable in this organic solvent, allowing the mixture to gel, and calcining the resulting carbonaceous gel (Japanese Patent Application Laid-open No. Hei (5(1993)-320662); a method comprising treating a carbonaceous material such as raw coke with an oxidizing agent to introduce a functional group, causing the oxidizing product to come into contact with a metal salt, and calcining the resulting product in an inert atmosphere (Japanese Patent Application Laid-open No. Hei 6(1994)-40771); and the like. All these methods require oxidizing a raw material with an oxidizing agent such as nitric acid to introduce a functional group. To introduce a sufficient amount of functional groups it is necessary to use several tens times as much oxidizing agent as the amount of the raw material, requiring large equipment and a high cost for washing the product obtained by the oxidation treatment and for treating waste fluid. In addition, when a high-softening-point pitch such as a mesophase pitch is used as a raw material, manufacture of this mesophase pitch itself requires complicated processing such as heat treatment at high temperature and polymerization using a catalyst, which make the manufacturing process unstable and increase the production cost.
On the other hand, as the method using an organic compound which originally possesses a functional group as a starting material, a method is proposed comprising emulsion polymerizing an .alpha.,.beta.-unsaturated monomer containing specific functional group to obtain polymer particles, causing a metal in the form of a metal complex to bond as a ligand with the specific functional group existing on the surface, and calcining the resulting product (Japanese Patent Application Laid-open No. 5(1993)-98302). This method can utilize only the functional groups existing on the surface of polymer particles. Accordingly, the method can be carried only on the surface of the carbonaceous material.